Numerous regulatory agencies dealing with building safety have established different safety classifications for different electrical circuits and communication transmission pathways. The highest level of safety class is “class X” (see 12.3.6 NFPA 72 2010 safety regulation). In order to obtain a “class X” classification, the following requirements must be meet:                All circuits have a redundant path.        Circuit paths between the Fire Alarm Central Unit (FACU) and remote peripherals shall continue to operate flawlessly under the condition of a single open or a single short circuit condition.        Circuit paths shall be monitored and supervised to detect and annunciate a short or open circuit condition.Thus, FACU and remote peripherals must be monitored and any short or open circuit conditions must be annunciated in order to fulfill the requirements of the “class X” performance criteria.        
As redundant circuits are typically routed via different physical transmission pathway locations for the obvious safety reasons; the propagation delays experienced on one pathway versus another will vary. Real world cable propagation delays of five nanoseconds per meter or more preclude a simple solution of combinatorial logic being implemented on the redundant received data lines of the two pathways to arrive at a desired logic level for the desired bit time.
Currently, simplistic approaches have been used to detect open or short conditions in a circuit. Such approaches detected the fault and provided little or no additional information. In a fire or disaster, additional information enables first responders to better understand where problems or dangers may exist. Maintainers of a redundant bus system may also benefit from additional information when an error is detected in a system and more quickly correct detected faults. Therefore, there is a need for an approach that not only detects a short or open circuit, but provides additional information that may aid in correcting the fault or identifying at risk areas during an emergency.